Field of the Invention
The present invention relates to a diamond-like carbon film-formed material, which contains a substrate and a diamond-like carbon film formed on a surface thereof with an intermediate layer therebetween, and a method for producing the same.
Description of the Related Art
As is well known, a diamond-like carbon (hereinafter referred to also as DLC) film is composed of an amorphous carbon, has high hardness and low friction coefficient, and thereby has been used as an abrasion-resistant lubricant film on various substrates. Specifically, the DLC film has been used as a surface coating of a magnetic disk reading head, a working tool, etc. Known methods for forming the DLC film include plasma chemical vapor synthesis (CVD) methods, sputtering methods, arc ion plating methods, etc.
The bonding strength between the DLC film and the substrate is not very high, and the DLC film tends to be readily peeled off from the substrate. Therefore, various studies have been made on the prevention of the peeling of the DLC film.
For example, proposed in Japanese Laid-Open Patent Publication No. 10-203897 is a method for cleaning a surface of a substrate, which contains the steps of irradiating the substrate with hydrogen ions to induce a reduction reaction of the surface, and then exposing the surface to a sputtering gas. However, when the substrate is composed of a substance that cannot be readily converted to a carbide (such as aluminum, magnesium, silicon, or an alloy thereof), it is difficult to prevent the peeling of the DLC film even in the case of using thus cleaned surface.
Japanese Laid-Open Patent Publication No. 10-203897 describes, in the paragraph 0023, a method, which contains the steps of implanting carbon ions into a substrate to form a carbon-containing layer as an ion-implanted layer, and thereafter forming a DLC film thereon. However, in this method, the carbon-containing layer is formed inside the substrate, and probably the surface composition of the substrate is hardly changed by the ion implantation. Therefore, it is difficult to maintain a satisfactory bonding strength between the DLC film and the surface, and thus to prevent the peeling of the DLC film.
Another proposed method for preventing the peeling of the DLC film contains disposing an intermediate layer between the substrate and the DLC film. For example, Japanese Laid-Open Patent Publication No. 10-203896 describes a method containing the steps of forming an adhesion layer composed of silicon, tungsten, titanium, or aluminum and a DLC pretreatment layer composed of silicon carbide, tungsten carbide, titanium carbide, or aluminum carbide in this order on a surface of the substrate, and forming the DLC film on the DLC pretreatment layer.
In addition, Japanese Laid-Open Patent Publication No. 2008-024996 describes a method containing the steps of forming a metal-containing DLC layer as the intermediate layer on a substrate composed of an alloy of aluminum, magnesium, or titanium, and then stacking the DLC film and the metal-containing DLC layer alternately. The metal in the metal-containing DLC layer is tungsten, molybdenum, chromium, or titanium, and the content of the metal is 5% to 15% by weight.
When the intermediate layer is formed as described above, a target and equipment for generating a metal for the intermediate layer are required as shown in FIG. 2 of Japanese Laid-Open Patent Publication No. 10-203896 and the paragraph 0031 of Japanese Laid-Open Patent Publication No. 2008-024996. Thus, the film formation apparatus has a complicated large structure, resulting in high equipment costs disadvantageously.